PARTIAL CHARACTERIZATION OF A NON-PROTEINACEOUS SUPPRESSOR OF NONSPECIFIC ELICITORS FROM CLADOSPORIUM-FULVUM (SYN FULVIA-FULVA)

It is our working hypothesis that suppression of the activity of glycoprotein non-specific elicitors (NSE) from fungal cell walls is required in establishment of basic compatibility in the Cladosporium fulvum-tomato system. A suppressor of NSE-induced necrosis on tomato leaves was partially purified from intercellular fluid (IF) obtained from C. fulvum infected, or uninoculated, leaves. The suppressor was stable to treatment with heat, protease, glucosidase, galactosidase, laminarinase, periodate, and mild acid (0·1 N HCl) and base (0·01 N NaOH). Addition of the chelators, EDTA (15 mM) or EGTA (2 mM), to IF resulted in a marked reduction in suppressor activity. Suppressor activity was partially reduced by dialysis of IF, but activity was lost upon dialysis by prior treatment of IF with urea, or with protease which was then inactivated by heating. Activity of a low molecular weight suppressor, partially purified by dialysis and Sephadex G-25 column chromatography, corresponded with a carbohydrate peak. Pectinase or pectinase-generated oligogalacturonides from polypectate suppressed activity of NSE. However, incubation of NSE with pectinase, followed by heat treatment before assay, did not affect NSE activity. It is suggested that low molecular weight suppressor molecules may originate from action of pectolytic enzymes on host cell walls. In addition to these low molecular weight suppressor, native IF, but not heat treated IF, contained proteins that on in vitro incubation with NSE slowly reduced its ability to induce necrosis. © 1993 Academic Press, Inc.